(a) Technical Field
Embodiments of the present disclosure relate generally to a drive motor for an environmentally friendly vehicle, and more particularly, to a stator winding pattern of a hairpin drive motor capable of minimizing a maximum potential difference at an adjacent section between phases in a hairpin drive motor.
(b) Description of the Related Art
In general, environmentally friendly vehicles, such as a hybrid vehicle or an electric vehicle, may generate a driving torque by an electric motor (hereinafter referred to as “drive motor”) for obtaining a rotating force based on electrical energy. A hybrid vehicle can run in an electric vehicle (EV) mode (i.e., a pure electric mode) using only power of a drive motor or a hybrid electric vehicle (HEV) mode using driving torques of both an engine and a drive motor for power. Meanwhile, an electric vehicle runs using solely the torque of the drive motor as power.
For example, a drive motor used as a power source for an environmentally friendly vehicle is generally a permanent magnet synchronous motor (PMSM). The drive motor as a PMSM typically includes a stator to generate a magnetic flux, a rotor spaced apart from the stator by a predetermined gap, and a permanent magnet installed at the rotor. The stator includes a plurality of slots which are formed at an inner peripheral portion of a stator core, and a stator coil is wound in the slots. Accordingly, if an AC current is applied to a stator coil, the stator generates a rotation magnetic field so that a rotation torque may be generated in the stator due to the rotation magnetic field.
Meanwhile, the drive motor is classified into a distribution winding drive motor and a concentrated winding drive motor depending on a winding scheme of the stator coil. A stator of the distribution winding drive motor is divided into a segment coil stator and a distribution winding coil stator according to a winding scheme of the coil. The segment coil stator is a stator for inserting a coil in a slot of a stator core after primarily molding the coil to have a predetermined shape in advance. The distribution winding coil stator inserts a coil assembly in a slot of the stator core.
Output of the drive motor is proportional to the number of turns of a coil wound in the stator core. However, if the number of turns of the coil is increased, the size of the stator core or the motor is inevitably increased which results in reduction in miniaturization. Accordingly, in order to improve the output of the motor without increasing the size of the motor, a method of increasing a space factor of a coil wound around the stator core (e.g., by minimizing a dead space between the stator core and a winding coil) may be considered.
In this regard, in place of using a ring-shaped coil (i.e., “ring-shaped wire”) having a circular section as a coil winding, a method of using a flat coil (i.e., “flat wire”) having a square section has been actively studied. The flat coil may reduce the dead space and improve the space factor due to a shape of a section as compared with the ring-shaped coil. However, the flat coil has a difficulty in a coil winding work as compared to the ring-shaped coil. This is because the flat coil is manufactured to have a wide cross-section as compared with the ring shaped coil in order to maximize the space factor so it is difficult to use a winding machine.
Accordingly, methods have been proposed for easily performing coil winding work of the flat coil in a segment stator of the distribution winding drive motor, in which a plurality of separated hairpins (i.e., U-shape or V-shape) are inserted and engaged into each slot of the stator core, and in which sequentially welds between hairpins disposed in the slot are formed to continuously form a coil winding of the stator core. A motor including a coil winding formed in this way is conventionally referred to as a “hairpin drive motor.” The coil winding structure of the hairpin drive motor overcomes a device limit due to a winding machine and coil winding work is easily possible in a case of the flat coil, and may implement a miniaturized motor with high power by increasing the space factor of the coil.
Since the hairpin drive motor described above is configured with a continuous winding by inserting a leg of the hairpin in a slot of the stator core and welding an adjacent leg in a radial direction in the slot, a section adjacent to a hairpin on a different phase is generated. Insulation is weak in the above section so that there is a need for a separate insulation structure. Meanwile, in a conventional stator winding structure of a hairpin drive motor, if a rotating direction of the motor and a draw out position of one phase (e.g., a U-phase) are determined, a position of a different phase (e.g., V-phase or W-phase) may be determined in each slot with a predetermined pattern. In this case, a 3-phase draw out part and a neutral point draw out part may be formed as a pattern of a rule minimizing a pitch between phases in order to simplify a winding structure of a hairpin by reducing a draw out length of the winding coil.
However, since a conventional 3-phase draw output part has a coil winding structure minimizing a patch between phases, a section adjacent to a hairpin of different phases is generated in an insertion direction of the hairpin inserted into a slot of the stator. Therefore, a section having a maximum potential difference is located in the adjacent section between phases, thereby causing an insulation problem of the motor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.